More particularly, the electrical connection interconnects first and second metal parts of a rotorcraft electrically, and optionally also mechanically. In general, the techniques that enable an electric current to pass from one electrically insulated metal part to another are referred to by the person skilled in the art as “metallization”.
The airframe of a rotorcraft represents the reference electric potential of the rotorcraft, so it is essential for the various pieces of rotorcraft equipment to be electrically connected to said airframe. This grounding of equipment then serves to provide protection against various disturbances, lightning, static electricity, or indeed atmospheric interference, for example.
The airframe of a modern rotorcraft is often made of composite materials, so manufacturers provide metal parts that provide electrically conductive pathways in the panels of the airframe and they then connect the pieces of equipment of the rotorcraft to these electrically conductive pathways.
Unfortunately, two metal parts are often electrically insulated relative to each other. This applies in particular when the outside faces of the metal parts are covered in paint or when grease is placed between said outside faces.
Thus, unless special precautions are taken, these two adjacent metal parts, a piece of equipment, and an electrically conductive pathway will all be electrically insulated relative to one another and they will thus not be electrically interconnected. This situation can also arise when it is desired to fasten one piece of equipment on another piece of equipment, e.g. a filler valve on its support.
Consequently, the electric current generated by lightning and received by a first metal part of a piece of rotorcraft equipment is not conveyed to the rotorcraft airframe by a second metal part even if the first and second metal parts are in contact with each other. Since the first metal part is not connected to the reference potential of the rotorcraft, it is probable that the first metal part will be damaged by the lightning.
It is therefore appropriate that the connection between two metal parts, a piece of equipment, and an electrically conductive pathway, or indeed between two distinct pieces of equipment, for example, can serve firstly optionally to interconnect the two metal parts mechanically, and secondly allow an electric current to flow from one metal part to the other.
In order to remedy that technical problem, the person skilled in the art generally makes use of clamping means screwed into the first and second metal parts.
More precisely, the first metal part has a first top face and a first bottom face, while the second metal part has a second top face and a second bottom face.
Consequently, the first bottom face of the first metal part needs to be in contact with the second top face of the second metal part. In addition, it is appropriate for the first and second metal parts to be electrically interconnected, e.g. because they are coated in paint that insulates them electrically.
The person skilled in the art then drills the first and second metal parts, taps a thread in the holes drilled and interconnects the first and second metal parts by clamping means, e.g. a screw.
Once in the clamping position, the clamping means are thus in contact with the metal of both the first and the second metal parts, insofar as it is screwed into the metal portions of said metal parts.
Consequently, the clamping means provide the electrical connection between the first metal part and the second metal part. Electric current can then pass from the metal portion of the first metal part towards the clamping means, and then from the clamping means towards the metal portion of the second metal part.
The first and second metal parts are thus interconnected electrically in spite of the fact that the metal parts are electrically insulated relative to each other.
Nevertheless, that technique can turn out to be insufficient.
The person skilled in the art then sometimes coats the clamping means in a deposit of aluminum in order to improve electrical connection. Although effective, that solution is nevertheless insufficient for passing a high level of electric current, since the threads of the clamping means covered in the aluminum deposit provide a surface area that is not sufficient for passing the current.